osPID Sous Vide: Open source high tech cooking on a budget

It seemed inevitable that I’d put together a sous vide immersion cooker, when I came across a post regarding the osPID I knew the time was right. The osPID or Open Source Proportional–Integral–Derivative Controller is a device which can be employed to turn a heater on and off in such a way as to keep the temperature of an environment at a specific level — in this case a container of water used to cook sealed food, or a sous vide.

What I liked about the osPID is that it’s more than just a PID, it’s a platform. Programmable as any Arduino is along with four buttons, a two line LCD display (my favourite white-on-blue style) and limitless expansion possibilities, the osPID can be used in many, many applications — a sound investment I thought, so I invested. Can anyone spot the other PID in the gallery?

Commercial sous vide cookers can be extremely expensive. Creating one yourself is easy, it can be taken apart for storage and you can also salvage parts from it for other projects if need be.

Alternate Parts

Once I had the osPID up and running, thanks to great support from Brett (one half of the dynamic duo responsible for the osPID), I cut the black (hot) wire of the extension cord and attached each stripped end to the relay onboard the osPID. By using an extension cord I can plug any type of heater into the relay, for this project I purchased two Norpro Water/Tea/Coffee Heaters which have a useful clip style base. Because the extension I wired only had one outlet I needed a power bar to plug both heaters in — whether or not you’ll need one will depend on how many heaters you want to use.

I then purchased a K-Type thermocouple (don’t ask me what it means, K-Type is what the osPID supports), removed the connector it came with and connected the positive and negative leads to the thermocouple terminals on the osPID. These terminals are polarized so keep track of positive and negative leads on the thermocouple while working.

That’s it really. I purchase a circulation pump to keep the water moving in the vessel and thus heating evenly. I try to include a coat hanger in every project so I used one to suspend the ziplock full of tenderloin secured with a clip in the sous vide.

Keep in mind the thermocouple will most likely not read the proper temperature until calibrated so just use a thermometer to find the target temperature and set the osPID accordingly. For me an input reading of 57 translated to the 130°F I needed for medium rare, so I set the osPID to maintain an input of 57.

I would’ve preferred a larger bowl and will track one down, but the Beef Tenderloin With Lemon-Parsley Butter I cooked with my favourite gal turned out fantastic and we’re looking forward to more sous vide meals.

Thanks to Brett for the swift support and for the osPID itself.

Update: The Norpro Heaters stopped working on my second cook. This is probably due to the fact that I plugged them in before fully submersing the coils, that being said, many others have had these types of cheap immersion heaters die on them — so I included an alternate upgraded heater for those wishing to avoid the issue. Thankfully since I wired in a cord not the heaters themselves I was able to plug in another heat source for the osPID to control in order to get my dinner cooked.

Update: To replace the Norpro Heaters I picked up a couple of heating elements at a local electronic surplus store (Active Surplus) for $3 each. I snipped and soldered the Norpro power cords to the new heating elements and covered the connections with heat shrink tubing. You can see the final results in the gallery above. These weren’t stainless steel but they work just fine, I bent them to follow the curve of the bowl (which I’ll probably regret when I switch to another container) and to keep them from slipping I fashioned some clips out of, you guessed it, left over coat hanger. They’ll probably short circuit if both solder joints hit the water, heat shrinking or no – be mindful of that if you decide to go this route. I believe these are somewhere around 140 Watts, I needed both to maintain a temperature setting.

13 Comments.

FYI, I was suspicious of your temperature reading so I looked up the conversion. 57 degrees Celsius is 134 degrees Fahrenheit, so it would appear that the unit is designed to read in Celsius. A minor firmware change would convert it to what you would expect.

Also, I’ve never calibrated a K type thermocouple. I used to work for a forklift company and we made our own thermocouples from a spool of K-type wire and a bin of those yellow connectors you see on the commercial units. We would just strip the ends, twist the ends of the wires together, add the connector on the opposite end, and plug it in. Worked great every time. I’ve done this many times and never noticed enough error to worry about.

thermocouples aren’t calibrated, you must learn the thermocouple current at 0C and 100C then apply some math to learn what the current should be at, say, 57C.

They’re going to be *very* close to each other, individual thermocouples, so I wouldn’t worry a great deal about it unless you need sub-degree precision.

the ‘k’ type refers to the metals that are inside. Different metal combinations produce different currents and are more or less susceptible to temperature differences, and so on. the K type is the most common, as far as I know.

Nice writeup. Two tips from my experience:
Next time, leave the butter out of the bag! Any added fat will act as a solvent for good flavor. There’s a neat experiment somewhere on the web (can’t find it now) showing how flavor suffers if you add butter to the sous vide steak.
Another sidenote: it it vital to not use an immersion heater but a ‘dumb crockpot’ or something similar (thus something that shuts itself down on overheating), because if you forget an immersion heater that doesn’t have a water level sensor you might just burn your house down. (Almost happened to me.)
Also: Try to get a good thermometer to check the calibration of the thermometer. There’s quite some room for error if the temperature is stable, but if you want predictable results, it’s nice to know at exactly what temp you are working. (I like 56.5 deg C best for my steak.)

To my knowledge you shouldn’t have to waterproof the thermocouple. By flat do you mean no reading or the reading doesn’t change? Are you using the osPID or another? Try adding some boiling water to see the effect on the thermocouple’s reading and ensure that you have the polarity correct when connecting it to your relay.

It’s not that expensive (~$150) considering it comes with a temp probe already and 4 programmable outlets (where you can plug the heaters and the pumps — you can even have two pumps run one after the other for a wave effect). It has a built-in web server (that lets you control see graphs on any web browser) and an iPhone/iPad app is available (called “Apex”).